Commercial and institutional kitchens are equipped to prepare food for large numbers of people and may form part of or adjoin larger facilities such as restaurants, hospitals and the like. Such kitchens are typically equipped with one or more commercial duty cooking units capable of cooking large amounts of food. On such a scale, the cooking process may generate substantial amounts of cooking heat and airborne cooking by-products such as water vapor, grease particulates, smoke and aerosols, all of which must be exhausted from the kitchen so as not to foul the environment of the facility. To this end, large exhaust hoods are usually provided over the cooking units, with duct work connecting the hood to a motor driven exhaust fan located outside the facility such as on the roof or on the outside of an external wall. As the fan is rotated by the motor, air within the kitchen environment is drawn into the hood and exhausted to the outside atmosphere. In this way, cooking heat and cooking by-products generated by the cooking units follow an air flow path defined between the cooking units and outside through the hood to be exhausted from the kitchen before they escape into the main kitchen environment and perhaps into the rest of the facility.
In many conventional installations, the motor driving the exhaust fan rotates at a fixed speed. The exhaust fan thus rotates at a fixed speed as well and, therefore, tends to draw air through the hood at a constant or fixed volume rate without regard to the amount of heat or cooking by-product actually being generated. As a result, there are often times throughout a working shift where the system may be under or over-exhausting. Under-exhausting allows heat and/or cooking by-products to build up in the kitchen or other parts of the facility, which can create discomfort and also overload the building heating and ventilation or air conditioning systems (“HVAC”). Similarly, over-exhausting wastes air that has been conditioned by the building HVAC, thus requiring further burden on the HVAC systems to make up the loss. Over-exhausting also results in energy inefficiencies with regards to the system in which the fixed speed that the exhaust fan is operating exceeds what is necessary to adequately remove heat or cooking by-product from the kitchen.
In other conventional installations, the motor driving the exhaust fan rotates based on feedback received from temperature sensors positioned in the exhaust hood. An increase in temperature of the exhaust hood is indicative of an increase heat and/or cooking by-products located in the exhaust hood. The motor driving the exhaust fan then increases its speed so that an under-exhaust condition is avoided. However, the cooking units may have additional parameters that are favorable to the exhaust of the heat and/or cooking by-products so that an increase in the speed of the exhaust fan due to an increase in temperature actually results in an over-exhaust condition. Thus, unnecessary energy is devoted to the system during over-exhausting which translates to an unnecessary increase in cost associated with removing heat or cooking by-product from the kitchen.